Forward error correction with parallel error detection for flash memories

ABSTRACT

Methods, systems, and devices are described for forward error correction for flash memory. Encoded data from flash memory may be used to generate a number of data streams. At each of a number of error detection sub-modules operating in parallel, a different one of the data streams is processed. Each error detection sub-module may detect whether a portion of the respective received stream contains an error, and forward the portion to an error correction module. The error correction module, physically separate from the error detection sub-modules, may correct the forwarded portions of the respective received streams containing an error. The age and error rate associated with the flash memory may be monitored, and a coding rate or other aspects may be dynamically adapted to account for these factors.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/858,510, filed on Aug. 18, 2010, titled “FORWARD ERROR CORRECTIONWITH PARALLEL ERROR DETECTION FOR FLASH MEMORIES”, which claims priorityto U.S. Provisional Patent Application No. 61/234,911, filed Aug. 18,2009, entitled “FORWARD ERROR CORRECTION FOR FLASH MEMORIES”, both ofwhich are hereby expressly incorporated by reference, as if set forth infull in this document, for all purposes.

BACKGROUND

The present invention relates to forward error correction (FEC) ingeneral and, in particular, to FEC for flash memory. The advancements offlash memory technology in recent years has dramatically increasedstorage capacity and decreased the cost of non-volatile semiconductormemory. This has made Solid State Drives (SSDs) (typically a flashmemory-based non-volatile memory system) an emerging substitute formagnetic Hard Disk Drive (HDD).

The use of FEC to enhance the reliability and longevity of flash memoryis one of the challenges for making SSDs perform on par with HDDs.

SUMMARY

Methods, systems, and devices are described for forward error correctionfor flash memory. Encoded data from flash memory may be retrieved togenerate a number of data streams (which may, but need not be, partiallydecoded). At each of a number of error detection sub-modules, adifferent one of the data streams is processed. Each error detectionsub-module may detect whether a portion of the respective receivedstream contains an error, and forward the portion of the respectivestream containing an error to an error correction module. An errorcorrection module may correct the forwarded portions of the respectivestreams.

The age and error rate associated with the flash memory may bemonitored, and a coding rate may be dynamically adapted to account forthese factors. The error rate may be monitored on a per-sector basisand, therefore, the coding rate may be adapted on a per-sector (orper-set of sectors) basis. As the error rate increases in certain setsof sectors, additional error-correction sub-modules assigned to thosesectors may be powered-up to handle the increased error rate. In oneexample, there are fewer error correction sub-modules than errordetection sub-modules; each error correction sub-module may betime-shared by a number of error detection sub-modules. Also, it isworth noting that the associations between flash memory sectors, errordetection sub-modules, and error correction sub-modules may be changeddynamically in response to age and error rates, as well.

BRIEF DESCRIPTION OF THE DRAWINGS

A further understanding of the nature and advantages of the presentinvention may be realized by reference to the following drawings. In theappended figures, similar components or features may have the samereference label. Further, various components of the same type may bedistinguished by following the reference label by a dash and a secondlabel that distinguishes among the similar components. If only the firstreference label is used in the specification, the description isapplicable to any one of the similar components having the same firstreference label irrespective of the second reference label.

FIG. 1 is a block diagram of a flash memory decoder system according tovarious embodiments of the invention.

FIG. 2 is a block diagram of a flash memory decoder according to variousembodiments of the invention.

FIG. 3 is a block diagram of a flash memory decoder system illustratingerror detection and correction sub-modules according to variousembodiments of the invention.

FIG. 4 is a block diagram of a flash memory decoder system illustratingan architecture for a decoder controller according to variousembodiments of the invention.

FIG. 5 is a flowchart illustrating a method of decoding data from aflash memory according to various embodiments of the invention.

FIG. 6 is a flowchart illustrating a method of age responsive decodingof data from a flash memory according to various embodiments of theinvention.

FIG. 7 is a flowchart illustrating a method of decoding data from aflash memory responsive to error rate according to various embodimentsof the invention.

DETAILED DESCRIPTION

Methods, systems, and devices are described for forward error correctionfor flash memory. Encoded data from flash memory may be processed togenerate a number of data streams. At each of a number of errordetection sub-modules operating in parallel, a different one of the datastreams is processed. Each error detection sub-module may detect whethera portion of the respective received stream contains an error, andforward the portion to an error correction module. An error correctionmodule, physically separate from the error detection sub-modules, maycorrect the forwarded portions. The age and error rate associated withthe flash memory may be monitored, and a coding rate or other aspectsmay be dynamically adapted to account for these factors.

This description provides example embodiments only, and is not intendedto limit the scope, applicability, or configuration of the invention.Rather, the ensuing description of the embodiments will provide thoseskilled in the art with an enabling description for implementingembodiments of the invention. Various changes may be made in thefunction and arrangement of elements without departing from the spiritand scope of the invention.

Thus, various embodiments may omit, substitute, or add variousprocedures or components as appropriate. For instance, it should beappreciated that in alternative embodiments the methods may be performedin an order different from that described, and that various steps may beadded, omitted, or combined. Also, features described with respect tocertain embodiments may be combined in various other embodiments.Different aspects and elements of the embodiments may be combined in asimilar manner.

It should also be appreciated that the following systems, methods, andsoftware may individually or collectively be components of a largersystem, wherein other procedures may take precedence over or otherwisemodify their application. Also, a number of steps may be requiredbefore, after, or concurrently with the following embodiments.

Although much of the following discussion relates specifically to flashmemory, aspects of the inventions are applicable to other forms of solidstate memory. Generally, there are two predominant types of flash memoryarchitectures: NOR and NAND. For the purposes of this disclosure, muchdiscussion is directed to NAND-type flash, while again noting thatprinciples set forth herein have wider applicability.

There are two primary NAND flash technologies. The earlier versions ofNAND flash were Single-Level Cell (SLC). With SLC Flash, there is onlyone programmed state in addition to the erased state. The total of twostates allows a single data bit to be stored in the memory cell. Thedesire for higher density led to the more advanced Multiple-Level Cell(MLC). With MLC flash, there are multiple programmed states in additionto the erased state which allows multiple bits to be stored per memorycell.

Because of this increase in density and the related issues inmanufacturing, one of the challenges for flash memory is to maintainhigh reliability and longevity. The deterioration of the oxide overtime, and the disruptions from neighboring memory pages, can lead todata retention and corruption issues translating into bit errors. Whilethe chances of any given data bit being corrupted is quite small, thevast number of data bits in a storage system makes the likelihood ofdata corruption a very real possibility. FEC may be one of the toolsused to address these bit errors to improve the reliability and lifespanof flash memory.

Systems, devices, methods, and software are described for FEC for flashmemory. Turning first to FIG. 1, a flash memory system 100 isillustrated. The system includes an encoder 105, flash memory 110, adecoder 115, and a controller 120. This flash memory system 100 may be astand-alone device, or may be integrated (in whole or in part) with acomputer, server, phone or mobile device, tablet, television, or anyother computing device.

Each of these system 100 components may be in communication with eachother. The encoder 105, decoder 115, and controller 120 may,individually or collectively, be implemented with one or moreApplication Specific Integrated Circuits (ASICs) adapted to perform someor all of the applicable functions in hardware. Alternatively, thefunctions may be performed by one or more other processing units (orcores), on one or more integrated circuits. In other embodiments, othertypes of integrated circuits may be used (e.g., Structured/PlatformASICs, Field Programmable Gate Arrays (FPGAs), and other Semi-CustomICs), which may be programmed in any manner known in the art. Thefunctions of each unit may also be implemented, in whole or in part,with instructions embodied in a memory, formatted to be executed by oneor more general or application-specific processors.

The encoder 105 may receive data to be stored, and encode the data(e.g., adding parity information) for storage in the flash memory 110 asencoded data. The decoder 115 may include a number of sub-components(not shown). An embodiment of the decoder 115 includes an errorcorrection module in communication with and physically separate from anerror detection module. The decoder 115 may process the encoded data togenerate a number of data streams (which may, but need not be, decodedin whole or in part). The decoder 115 may process each stream at adifferent error detection sub-module operating in parallel in thedecoder 115. Each error detection sub-module may detect whether aportion of the respective received stream contains an error, and thenforward the portion of the respective received stream containing anerror to the error correction module. The error correction module maycorrect the forwarded portions of the respective received streamscontaining an error.

There are a number of different FEC schemes and codes that may be usedin the flash memory system 100 introduced above. The system 100functionality may be also be leveraged in a number of ways. For example,the error detection module may detect and flag bit errors, and this mayallow sectors of memory with errors exceeding a threshold amount to beavoided by replacing such sectors with other sectors from a pool ofavailable substitutes. The encoder 105 may, also or alternatively,change the code rate for the error-laden sections. As flash become moredense, the inherent bit error probability becomes higher.

Some simple FEC coding may be used to clean up these errors. The HammingCode, with correction capacity of 1 bit and detection capability of 2,may be used with flash memory 110. With the desire for improving theperformance, as well as the increased probability of inherent bit errorsbecause of the denser memories, Bose Chaudhuri Hocqunghem (BCH) codesmay be used, including the binary BCH and non-binary BCH (Reed Solomon(RS)) codes. These codes offer a higher correction capacity incomparison to the Hamming Code.

BCH encoding/decoding architectures may be the foundation of errorcorrection in flash memory. However, there are more advanced codingoptions that may in some instances provide better performance than BCHcodes. These codes may be used in flash memory 110, particularly forhigher density flash and in applications where performance demandsincrease. Convolutional Turbo Codes (CTCs), Turbo Product Codes (TPCs),and low density parity check codes (LDPCs) are examples of the codingschemes that may be used. These state-of-the-art codes perform veryclose to the theoretical limits (Shannon Limits) of error correction,providing very high coding gain and improvement in Bit Error Rate (BER)performance for a given amount of redundancy.

Flash memory does have an inherent probability of error. Depending onthe flash technology, this error rate may typically be somewhere between1 e-5 and 1 e-8. To be able to match an HDD read/write bit error rate of1 e-15, a FEC scheme may be used. The measure of how good a job a codecan perform in increasing the reliability depends upon its correctioncapacity. If the probability of bit error for flash memory 110 is p andthe correction capacity of the code is t bits over a codeword length ofn bits, the probability of making an error may be expressed as:

$\begin{matrix}{p_{decoded} = {\sum\limits_{i = {t + 1}}^{n}{p^{i}*( {1 - p} )^{n - i}}}} & (1)\end{matrix}$

From equation (1), for a given p the higher the correction capacity ofthe code, the smaller the probability of error after the decoding willbe. The correction capacity can be expressed as the number of bits acode can correct over a codeword length, or an input BER, or probabilityof error that it can take down to a certain target decoded BER. Theadvanced codes may correct more errors over a certain length, or take ahigher input BER to create the same decoded BER.

There is incentive to use advanced codes for flash memory 110 even withnot so dense memories. If the inherent error performance of flash memory110 stayed at a certain low level, there would probably be decreasedneed for advanced codes. But, in practice, flash memory 110 performancetends to degrade over time. This means that even with an advanced codeto help improve the reliability of a flash memory 110, over time theflash memory 110 may become lossy and, once the error rate is highenough, it may be beyond repair by the code being used.

In one example, the rate of errors or age of the flash memory 110 may bemonitored, and the coding rate for data to be stored on the flash memory110 may be modified in response thereto. Thus, a more robust coding ratemay be used as the decoded error rate increases. The error monitoringmay take place on a per-sector basis, and the code rate modification maysimilarly take place on a per-sector basis. In another example, the rateof errors or age of the flash memory 110 may be monitored, and errorcorrection sub-modules may be powered-up in response thereto. Powersavings may be achieved by keeping certain error correction sub-modulesin an inactive mode until the flash memory reaches a certain age.

As noted, the flash memory 110 may be partitioned into a pool of smallfixed-size sectors, and FEC may be applied on a sector-by-sector basis.The flash memory 110 size may be defined by the number of sectors thatit contains. As there is a chance of sectors going bad over time, theremay be a reserve/spare sector pool that allows the controller to replacethe bad sectors by the spares as needed to extend the life of the flash.The error detection sub-module and error correction sub-modules may bedynamically assigned to various sectors, and the number powered-on maybe increased or decreased.

A wear leveling technique may be used bb to make sure that variousareas/sectors of the Flash “age” at a similar rate. Instead of the samesector being used over and over again, the read/writes are spread overmuch or the entire flash. And this translates into the probability ofany sector being good (p_(good)) may be substantially the same for thevarious sectors in flash memory 110. If the size of the flash is Nsectors and there are Δ spare sectors, the probability that the flash isstill usable after time t is:

$\begin{matrix}{p_{usable} = {\sum\limits_{i = N}^{N + \Delta}( {c_{i}^{N + \Delta}*( p_{good} )^{i}*( {1 - p_{good}} )^{N + \Delta - i}} )}} & (2)\end{matrix}$

p_(good) may be a function of use time for the flash memory 110 sector.This is a component that is dependent upon the correction capacity ofthe code used. Thus, even with the spare sectors and the wear-levelingtechnique, the codes may play a key role in the flash being usable aftera certain use time.

One of the concerns regarding advanced codes is how they fit into thesector sizes and overhead requirements of some flash memoryarchitectures. TPC and LDPC codes offer an excellent degree of freedomin selecting the various code parameters like information block size,coded block size, and correction capacity, and would allow customizationto suit any number of flash configurations.

FIG. 2 is a block diagram 200 of a flash memory decoder 115-a accordingto various embodiments of the invention. The flash memory decoder 115-amay, for example, be the decoder 115 of FIG. 1, although flash memorydecoder 115-a may be implemented in a number of other systems anddevices, as well. The flash memory decoder 115-a includes a decodermodule 205, an error detection module 210, and an error correctionmodule 215, and each of may be in communication with each other. In oneexample, the error detection module 210 includes a number of sub-modulesconfigured to detect errors on decoded streams of data. The errorcorrection module 215 may be physically separate from each errordetection sub-module, and may also include a number of sub-modules (eachof which may be time-shared by a number of error detection sub-modules.

These components and sub-modules therein may, individually orcollectively, be implemented with one or more Application SpecificIntegrated Circuits (ASICs) adapted to perform some or all of theapplicable functions in hardware. Alternatively, the functions may beperformed by one or more other processing units (or cores), on one ormore integrated circuits. In other embodiments, other types ofintegrated circuits may be used (e.g., Structured/Platform ASICs, FieldProgrammable Gate Arrays (FPGAs), and other Semi-Custom ICs), which maybe programmed in any manner known in the art. The functions of each unitmay also be implemented, in whole or in part, with instructions embodiedin a memory, formatted to be executed by one or more general orapplication-specific processors.

The decoder module 205 may receive encoded data from flash memory, andprocess the received encoded data to generate a number of data streams.In one embodiment, the decoder module processor may buffer,de-interleave, or perform certain aspects of the decoding process, anthereby generate decoded (or partially decoded) data streams. As noted,the error detection module 210 may include a number of error detectionsub-modules operating in parallel. Each (or a subset) of the errordetection sub-modules may receive a different one of the data streams,and evaluate the respective stream to determine whether a portion of thestream contains an error. Each error detection sub-module may forwardthe portion of the respective received stream containing an error to theerror correction module 215 (bypassing the error correction module 215with the error-free portions). The error correction module 215 correctsthe received portions of the respective received streams containing anerror. As noted above, the error correction module 215 may include anumber of sub-modules (each of which may be time-shared by a number oferror detection sub-modules).

FIG. 3 is a block diagram illustrating an example of an architecture fora flash memory decoder system 300 more particularly illustrating errordetection and correction sub-modules. The flash memory decoder system300 may, for example, be the system 100 of FIG. 1. The flash memorydecoder system 300 includes flash memory 110-a, a decoder module 205-a,an error detection module 210-a, an error correction module 215-a, acontroller 120-a, and an encoder 105-a. Each of these components may bein communication with each other.

The flash memory 110-a includes a number of different sets of one ormore active sectors 305. The decoder module 205-a includes a number ofdecoder sub-modules 310, and each decoder sub-module 310 may beassociated with a different set of sectors 305. The error detectionmodule 210-a includes a number of error detection sub-modules 315, andeach decoder sub-module 310 may be associated with a different set ofsectors 305. Thus, encoded data may be read from a set of one or more ofsectors 305 (e.g., sector(s) 305-a) by a decoder sub-module 310 (e.g.,decoder sub-module 310-a), and processed (e.g., buffered,de-interleaved, decoded to some extent, etc.) to generate a data stream.The data stream may be forwarded to an error detection sub-module 315(error detection sub-module 315-a). Thus, encoded data from a set of oneor more of sectors 305-a may be sent to an error detection sub-module315-a. Different sets of sectors 305 may each send their respective datavia different decoder sub-modules 310, as illustrated. In oneembodiment, each error detection sub-module 315 is distinct from eachother. In other embodiments, the decoder sub-module 310 and errordetection sub-module 315 may be integrated to varying degrees.

Each error detection sub-module 315 may evaluate the respective streamto determine whether a portion of the stream contains an error. Eacherror detection sub-module 315 may forward the portion of the respectivereceived stream containing an error to the error correction module 215-a(bypassing the error correction module 215 with the error-freeportions). The error correction module 215-a includes a number of errorcorrection sub-modules 320, each error correction sub-module 320responsible for handling the errors from a number of error detectionsub-modules 315 (e.g., error correction sub-module 320 may correcterrors from error detection sub-modules 315-a, -b, and -c). Errorcorrection sub-modules 320 may correct the received portions of therespective received streams containing an error. Each error correctionsub-module 320 may receive portions of streams with errors, and theseportion may have been detected in parallel.

Controller 120-a may perform a number of functions in the decoderprocess. Controller 120-a may dynamically modify the error detectionsub-modules 315 and the error correction sub-modules 320 assigned tosectors 305 of flash memory 110-a. The controller 120-a may selectivelypower-up one or more of the error correction sub-modules 320 responsiveto a monitored age or error rate associated with the flash memory 110-a.The controller 120-a may perform this monitoring on a per-sector basis,and the error correction sub-modules 320 may be powered-up to serve thesectors 305 where the error rates exceed a threshold. The controller120-a may adapt the coding rate to be used by the encoder responsive toa monitored age or error rate associated with the flash memory 110-a.The controller 120-a may perform this monitoring on a per-sector basis,and the controller 120-a may adapt the coding rate on a per sectorbasis.

FIG. 4 is a block diagram of a flash memory decoder system 400illustrating certain controller functionality according to variousembodiments of the invention. The system 400 includes an encoder 105-b,flash memory 110-b, a decoder 115-b, and a controller 120-b. This system400 may be an example of the system 100 of FIG. 1, and a component ofthis system 400 may have the same functionality as the counterpartcomponent from FIG. 1 This flash memory system 400 may be a stand-alonedevice, or may be integrated (in whole or in part) with a computer,server, phone, mobile device, tablet, television, or any other computingdevice.

The controller 120-b includes an adaptive encoding rate controller 405,a power controller 410, a write controller 415, a read controller 420,an age monitoring module 425, and an error monitoring module 430. Theage monitoring module 425 may monitor an age associated with the flashmemory 110-b. This may be a time since manufacture, a time since firstuse, an amount of use, or any other metric which corresponds to theaging of the flash memory 110-b. This monitoring may involve directmonitoring of the flash memory 110-b itself, or may be based on reportsfrom the encoder 105-b, decoder 115-b, or other components of thesystem.

The error monitoring module 430 may monitor an amount of errorsassociated with the flash memory 110-b. This monitoring may measureerrors over a variety of time periods and metrics, and may be translatedinto an error rate. The monitoring may be performed on a per-sector (orper set of sectors) basis. A number of sampling and averaging techniquesmay be used. This monitoring may involve direct monitoring of thedecoder 115-b itself, or may be based on reports from the decoder 115-bor other components of the system.

The adaptive encoding rate controller 405 may receive information on therate and/or amount of errors from the error monitoring module 430. Theadaptive encoding rate controller 405 may modify a coding rate to beused by the encoder 105-b when the monitored rate and/or amount oferrors exceeds a threshold. The monitoring of errors may be performed ona per-sector, per set of sectors, or other regional basis. Thus, thecoding rate to be used by the encoder 105-b may be modified when themonitored rate of errors for the applicable region exceeds a threshold.In some embodiments, the coding rate may be adapted to be more, or less,robust; in other embodiments, the adaptation is only to make the codingrate more robust. The adaptive encoding rate controller 405 may receiveinformation on the age of the flash memory 110-b from the age monitoringmodule 425. The adaptive encoding rate controller 405 may adapt thecoding rate based on this monitoring (e.g., implementing a more robustcoding rate for one or more sectors of the flash memory 110-b when theage exceeds a threshold). There may be a number of different coding ratechange thresholds related both to age and error rate. Moreover, thesethreshold may be adaptive to the amount of flash memory 110-b thatremains available (e.g., the margin may be increased when the flashmemory is utilized below a threshold amount).

As noted above, an decoder module 115 may include a number of errorcorrection sub-modules. The power controller 410 may receive informationon the age of the flash memory 100-b from the age monitoring module 425.The power controller 410 may selectively power-up (or power-down) one ormore of the error correction sub-modules responsive to an age of theflash memory 110-b. The power controller 410 may receive information onthe rate and/or amount of errors from the error monitoring module 430.The power controller 410 may power-up (or power-down) one or more of theerror correction sub-modules (e.g., when the monitored rate and/oramount of errors exceeds a threshold). The monitoring of errors may beperformed on a per-sector, per set of sectors, or other regional basis.Thus, the power-up or power-down may be specific to a particular errorcorrection sub-module for a given region of flash memory 110-b.

The write controller 415 may change the sectors of flash memory 110-b tobe written to. These changes may be made in response to information fromthe age monitoring module 425 and error monitoring module 430. The readcontroller 420 may dynamically change the components of the decoder115-b to be used to read different sectors of flash memory 110-b (e.g.,in FIG. 3, the assignments of the decoder sub-modules 310, errordetection sub-modules 315, and error correction sub-modules 320 may bechanged in response to code rate modifications, increased errors, orage).

FIG. 5 is a flowchart illustrating a method 500 of decoding data from aflash memory according to various embodiments of the invention. Themethod 500 may, for example, be performed in whole or in part by thesystem 100, 300, or 400 of FIG. 1, 3, or 4 or, more specifically, by thedecoder 115 of FIG. 1, 2, or 4.

At block 505, encoded data from a flash memory is received. At block510, the received encoded data is processed to generate a number of datastreams. The information for each data stream may be a wholly orpartially decoded before being forwarded to respective error correctionsub-modules. At block 515, at each of a number of error detectionsub-modules operating in parallel, a different one of the data streamsis processed. Each error detection sub-module is configured to: detectwhether a portion of the respective received stream contains an error,and forward the portion of the respective received stream containing anerror to an error correction module. At block 520, at the errorcorrection module physically separate from the error detectionsub-modules, the forwarded portions of the respective received streamscontaining an error are corrected.

FIG. 6 is a flowchart illustrating a method of age responsive decodingof data from a flash memory according to various embodiments of theinvention. The method 600 may, for example, be performed in whole or inpart by the system 100, 300, or 400 of FIG. 1, 3, or 4. The method 600may be an example of the method 500 of FIG. 5.

At block 605, an age of a flash memory is monitored. At block 610, thecoding rate for data to be encoded and stored in the flash memory ismodified responsive to a first age threshold of the flash memory. Atblock 615, data is encoded at the modified rate, and the encoded data isstored on the flash memory. At block 620, one or more error correctionsub-modules of an error correction module are powered-up from aninactive mode responsive to a second age threshold of the flash memory.

At block 625, the encoded data from the flash memory is processed togenerate a number of partially decoded data streams. At block 630, ateach of a number of error detection sub-modules operating in parallel, adifferent one of the data streams is processed. At block 635, adetermination is made at each error detection sub-module whether aportion of the respective received stream contains an error. At block640, error detection sub-modules forward those portions of therespective streams containing an error to the error correction modulephysically separate from the error detection sub-modules. At block 645,the error-free portions are forwarded to bypass the error correctionmodule. At block 650, the portions of the respective received streamscontaining an error are corrected with the powered-up error correctionmodules and additional error correction modules.

FIG. 7 is a flowchart illustrating a method of decoding data from aflash memory responsive to error rate according to various embodimentsof the invention. The method 700 may, for example, be performed in wholeor in part by the system 100, 300, or 400 of FIG. 1, 3, or 4. The method700 may be an example of the method 500 of FIG. 5 or the method 600 ofFIG. 6.

At block 705, a rate of errors from an error detection module ismonitored for each of a number of sectors of the flash memory. At block710, the coding rate for data to be encoded and stored in one or moresectors is modified responsive to the monitoring of first error ratethreshold for the one or more sectors. At block 715, data is encoded atthe modified rate and stored in the one or more sectors.

At block 720, an error correction sub-module assigned to the one or moresectors are powered-up from an inactive mode responsive to themonitoring of a second error rate threshold for the one or more sectors.At block 725, the encoded data from the one or more sectors is decodedto generate a decoded data stream. At block 730, at one of a number oferror detection sub-modules operating in parallel, the decoded datastream is processed. At block 735, a determination is made by the errordetection sub-module that a portion of the respective received streamcontains an error. At block 740, the portion of the received streamcontaining an error is forwarded to the powered-up error correctionsub-module. At block 745, the forwarded portion is corrected with thepowered-up error correction sub-module.

It should be noted that the methods, systems, and devices discussedabove are intended merely to be examples. It must be stressed thatvarious embodiments may omit, substitute, or add various procedures orcomponents as appropriate. For instance, it should be appreciated that,in alternative embodiments, the methods may be performed in an orderdifferent from that described, and that various steps may be added,omitted, or combined. Also, features described with respect to certainembodiments may be combined in various other embodiments. Differentaspects and elements of the embodiments may be combined in a similarmanner. Also, it should be emphasized that technology evolves and, thus,many of the elements are examples and should not be interpreted to limitthe scope of the invention.

Specific details are given in the description to provide a thoroughunderstanding of the embodiments. However, it will be understood by oneof ordinary skill in the art that the embodiments may be practicedwithout these specific details. For example, well-known circuits,processes, algorithms, structures, and techniques have been shownwithout unnecessary detail in order to avoid obscuring the embodiments.

Also, it is noted that the embodiments may be described as a processwhich is depicted as a flow diagram or block diagram. Although each maydescribe the operations as a sequential process, many of the operationscan be performed in parallel or concurrently. In addition, the order ofthe operations may be rearranged. A process may have additional stepsnot included in the figure.

Moreover, as disclosed herein, the term “memory” or “memory unit” mayrepresent one or more devices for storing data, including read-onlymemory (ROM), random access memory (RAM), magnetic RAM, core memory,magnetic disk storage mediums, optical storage mediums, flash memorydevices, or other computer-readable mediums for storing information. Theterm “computer-readable medium” includes, but is not limited to,portable or fixed storage devices, optical storage devices, wirelesschannels, a sim card, other smart cards, and various other mediumscapable of storing, containing, or carrying instructions or data.

Furthermore, embodiments may be implemented by hardware, software,firmware, middleware, microcode, hardware description languages, or anycombination thereof. When implemented in software, firmware, middleware,or microcode, the program code or code segments to perform the necessarytasks may be stored in a computer-readable medium such as a storagemedium. Processors may perform the necessary tasks.

Having described several embodiments, it will be recognized by those ofskill in the art that various modifications, alternative constructions,and equivalents may be used without departing from the spirit of theinvention. For example, the above elements may merely be a component ofa larger system, wherein other rules may take precedence over orotherwise modify the application of the invention. Also, a number ofsteps may be undertaken before, during, or after the above elements areconsidered. Accordingly, the above description should not be taken aslimiting the scope of the invention.

What is claimed is:
 1. A method comprising: encoding data using forwarderror correction coding; storing the encoded data in a flash memory;retrieving the encoded data stored in the flash memory to generate adata stream; processing, using at least a first error correctionsub-module, the data stream to correct errors in the data streamassociated with the flash memory; monitoring a metric of the flashmemory while repeating the encoding, the storing, the retrieving and theprocessing, wherein the metric represents memory performance degradationof the flash memory; determining that the monitored metric exceeds athreshold; in response to the determination, modifying the forward errorcorrection coding for use in subsequently encoding data for storage inthe flash memory; and in response to the determination, powering-up,from an inactive mode, a second error correction sub-module arranged inparallel with the first error correction sub-module for subsequent datastream processing.
 2. The method of claim 1, wherein the modifyingcomprises changing a coding rate of the forward error correction coding.3. The method of claim 1, wherein the modifying comprises implementingmore robust forward error correction coding.
 4. The method of claim 1,wherein the metric is based at least in part on an aging of the flashmemory.
 5. The method of claim 4, wherein the metric is based on one ormore of a time since manufacture of the flash memory, a time since firstuse of the flash memory, and an amount of use of the flash memory. 6.The method of claim 1, wherein the metric is based at least in part onan amount of errors corrected during the processing.
 7. The method ofclaim 6, wherein the metric is based on the amount of errors correctedover a period of time.
 8. The method of claim 1, wherein the retrieving,the processing and the monitoring are performed on a sector-by-sectorbasis of the flash memory.
 9. The method of claim 1, further comprising:subsequently encoding data using the modified forward error correctioncoding; and storing the subsequently encoded data in the flash memory.10. The method of claim 9, wherein the subsequently encoded data isstored in a sector of the flash memory different than that of saidencoded data.
 11. The method of claim 9, further comprising: retrievingthe subsequently encoded data stored in the flash memory to generate asecond data stream; and processing, using at least the first errorcorrection sub-module and the second error correction sub-module, thedata stream to correct errors in the data stream associated with theflash memory.
 12. The method of claim 1, wherein the threshold is basedat least in part on an amount of available memory within the flashmemory.
 13. A system comprising: an encoder to encode data using forwarderror correction coding; a flash memory to store the encoded data; adecoder to retrieve the encoded data stored in the flash memory togenerate a data stream, and to process the data stream to correct errorsin the data stream associated with the flash memory using at least afirst error correction sub-module; and a controller to: monitor a metricof the flash memory while repeating the encoding, the storing, theretrieving and the processing, wherein the metric represents memoryperformance degradation of the flash memory; determine that themonitored metric exceeds a threshold; in response to the determination,modify the forward error correction coding for use by the encoder insubsequently encoding data for storage in the flash memory; and inresponse to the determination, powering-up, from an inactive mode, asecond error correction sub-module arranged in parallel with the firsterror correction sub-module for subsequent data stream processing. 14.The system of claim 13, wherein the controller changes a coding rate ofthe forward error correction coding to modify the forward errorcorrection coding.
 15. The system of claim 13, wherein the controllerimplements more robust forward error correction coding to modify theforward error correction coding.
 16. The system of claim 13, wherein themetric is based at least in part on an aging of the flash memory. 17.The system of claim 16, wherein the metric is based on one or more of atime since manufacture of the flash memory, a time since first use ofthe flash memory, and an amount of use of the flash memory.
 18. Thesystem of claim 13, wherein the metric is based at least in part on anamount of errors corrected during the processing.
 19. The system ofclaim 18, wherein the metric is based on the amount of errors correctedover a period of time.
 20. The system of claim 13, wherein the decoderretrieves the encoded data and processes the data stream on asector-by-sector basis of the flash memory, and the controller monitorsthe metric on a sector-by-sector basis of the flash memory.
 21. Thesystem of claim 13, wherein: the encoder subsequently encodes data usingthe modified forward error correction coding; and the flash memorystores the subsequently encoded data in the flash memory.
 22. The systemof claim 21, wherein the flash memory stores the subsequently encodeddata in a sector different than that of said encoded data.
 23. Thesystem of claim 21, wherein the decoder: retrieves the subsequentlyencoded data stored in the flash memory to generate a second datastream; and processes, using at least the first error correctionsub-module and the second error correction sub-module, the data streamto correct errors in the data stream associated with the flash memory.24. The system of claim 13, wherein the threshold is based at least inpart on an amount of available memory within the flash memory.